1. Field of the Invention
The present invention relates to a method and apparatus for producing a photoelectric conversion device, and more particularly to a solar cell for converting light energy to electric energy and a method of producing the same.
2. Related Background Art
The emission of globe warming gases such as carbon dioxide, nitrogen oxides, or the like as generated by combustion of petroleum in thermal power generation or combustion of gasoline in automotive engines is responsible for worsening of the global environment. Further, there is a concern for future exhaustion of the crude oil. Thus, power generation by solar cells receives interest and attention as a clean energy source. The thin film crystalline silicon (Si) solar cell can be produced with a thin power generation layer using less Si starting material, so that the production cost can be reduced. Moreover, the thin film crystalline Si solar cell uses crystalline Si for a power generation layer and can therefore be expected to demonstrate a higher photoelectric conversion efficiency and less deterioration as compared with solar cells using amorphous Si or the like. In addition, the thin film crystalline Si solar cell can be bent to a certain degree and can therefore be applied to a curved surface of an automotive body, appliance, roofing tile, or the like.
In order to realize a thin film crystalline Si solar cell, Japanese Patent Application Laid-Open No. 8-213645 discloses utilizing an epitaxial layer on a porous Si layer to separate a thin film monocrystalline Si. FIG. 33 is a schematic sectional view illustrating a method of forming a thin film Si solar cell disclosed in Japanese Patent Application Laid-Open No. 8-213645. In the figure, reference numeral 2601 denotes a Si wafer; 2602 a porous Si layer; 2603 a p+-type Si layer; 2604 a pxe2x88x92-type Si layer; 2605 an n+-type Si layer; 2606 a protective layer; 2607 an adhesive; and 2608, 2609 a jig.
In the method of producing a solar cell illustrated in FIG. 33, firstly the porous Si layer 2602 is formed by anodization in a surface of the Si wafer 2601. Then, the p+-type Si layer 2603 is epitaxially grown on the porous Si layer 2602, and the pxe2x88x92-type Si layer 2604 and the n+-type Si layer 2605 are further epitaxially grown thereon, respectively. Subsequently, the protective layer 2606 is formed. Then, the adhesive is applied to the protective layer 2606 and the Si wafer 2601, and the jig 2608, 2609 is adhered thereto. After that, a pulling force is exerted to the jig 2608, 2609 to separate the Si wafer 2601 and the epitaxial layers 2603, 2604, 2605 at the porous layer 2602. Then, the epitaxial layers 2603, 2604, 2605 are used to form a solar cell, while the Si wafer 2601 is again put into the same production steps as mentioned above, thus attaining cost reduction.
However, in the method of Japanese Patent Application Laid-Open No. 8-213645, a pulling force is merely exerted to the jig 2608, 2609 to separate the Si wafer 2601 and the epitaxial layers 2603, 2604, 2605 at the porous layer 2602. With this method, it is not necessarily possible to make sure that the separation is effected at the porous Si layer 2602. When separated by the pulling force, the epitaxial layers 2603, 2604, 2605 may sometimes be broken or impaired. Thus, photoelectric conversion devices provided by this method may have a low yield or low product quality.
One of the objects of the present invention is to provide a method of separating a bonded substrate with a high yield, thereby providing a method and apparatus that can supply photoelectric conversion devices with a high quality at a low production cost.
In order to solve the above mentioned issue, the inventors have conducted extensive theoretical and laboratory studies and accomplished the present invention.
According to a first aspect of the present invention, there is provided a method of producing a photoelectric conversion device comprising the steps of: forming a semiconductor substrate comprising a first and a second semiconductor layers with a separation layer therebetween; bonding a support substrate to a surface of the second semiconductor layer opposite to the separation-layer-side surface to form a bonded substrate; separating the first and the second semiconductor layers by the separation layer; and producing a photoelectric conversion device in the second semiconductor layer, wherein when bonding the semiconductor substrate and the support substrate to each other, at least a portion is formed in the bonded substrate in which at least a part of end portions of the semiconductor substrate and the support substrate is not bonded to the other substrate and a fluid is jetted against a side surface of the bonded substrate, thereby separating the first and the second semiconductor layers.
In the method of producing a photoelectric conversion device of the first aspect of the present invention, it is preferred that the portion of the bonded substrate in which the semiconductor substrate and the support substrate are not bonded to each other is present in the vicinity of the separation layer and forms a recess such that the flow of the fluid is received by the recess to generate a force in such a direction as to expand the separation layer, and it is also preferred that the recess is formed by beveling the semiconductor substrate.
According to a second aspect of the present invention, there is provided a method of producing a photoelectric conversion device comprising the steps of: forming a semiconductor substrate comprising a first and a second semiconductor layers with a separation layer therebetween; bonding a support substrate to a surface of the second semiconductor layer opposite to the separation-layer-side surface to form a bonded substrate; separating the first and the second semiconductor layers by the separation layer; and producing a photoelectric conversion device in the second semiconductor layer, wherein when bonding the semiconductor substrate and the support substrate to each other, the bonding is carried out with the end portions of the semiconductor substrate and the support substrate being flush with each other and the fluid is jetted against a side surface of the bonded substrate, thereby separating the first and the second semiconductor layers.
In the methods of producing a photoelectric conversion device of the first and the second aspects of the present invention, it is preferred that the separation layer has a microvoid inside thereof, and it is also preferred that the separation layer is smaller in mechanical strength than the bonded portion of the support substrate and the semiconductor substrate.
Further, the semiconductor substrate may be formed by making partially porous a monocrystalline silicon substrate to form a separation layer as a porous monocrystalline silicon layer and epitaxially growing a monocrystalline silicon layer on the separation layer, wherein the separation layer may be formed by the anodization. Alternatively, the semiconductor substrate may be formed by providing a separation layer as a microbubble containing layer at a given depth in a monocrystalline silicon substrate, wherein the separation layer may be formed by the ion implantation.
Further, as a method for the jetting of a fluid, it is preferable to use the water jet method in which a flow of high-pressure water is ejected through a nozzle.
Moreover, the support substrate is preferably a light transmissive substrate.
In addition, the present invention encompasses an apparatus for producing a photoelectric conversion device. The apparatus for producing a photoelectric conversion device of the present invention comprises a holding member for holding a bonded substrate comprising a semiconductor substrate comprising a first semiconductor layer, a second semiconductor layer for producing a photoelectric conversion device therein, and a separation layer provided between the first and the second semiconductor layers, and a support substrate bonded to a surface of the second semiconductor layer opposite to the separation-layerside surface; and a nozzle for jetting a fluid against a side surface of the bonded substrate to separate the first and the second semiconductor layers by the separation layer.
In the present invention, the photoelectric conversion device includes a solar cell, a photosensor, or the like.
In the present invention, it is preferable to effect the separation after forming a semiconductor junction inside of the second semiconductor layer.
Further, it is preferable to effect the separation after removing a peripheral portion of the separation layer.
Moreover, it is preferable to use a nozzle as means for jetting a fluid and to jet the fluid against the bonded substrate while moving the nozzle parallel to the periphery of the bonded substrate. In this case, it is preferable that the periphery of the bonded substrate is of a polygonal shape, and that after jetting the fluid against the bonded substrate while moving the nozzle parallel to a side of the periphery, the bonded substrate is rotated, and the fluid is then jetted against the bonded substrate while moving the nozzle parallel to another side of the periphery.